1. Field of the Invention
The present invention relates to high operating temperature gold (Au) leads for a read sensor and, more particularly, to gold leads which will not flow out of a read head at the air bearing surface (ABS) when subjected to pressure and various temperatures under operating conditions.
2. Description of the Related Art
The heart of a computer is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, a slider that has write and read heads, a suspension arm above the rotating disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The write head includes a coil layer embedded in first, second and third insulation layers (insulation stack), the insulation stack being sandwiched between first and second pole piece layers. A gap is formed between the first and second pole piece layers by a nonmagnetic gap layer at an air bearing surface (ABS) of the write head. The pole piece layers are connected at a back gap. Current conducted to the coil layer induces a magnetic field into the pole pieces that fringes across the gap between the pole pieces at the ABS. The fringe field or the lack thereof writes information in tracks on moving media, such as in circular tracks on a rotating disk.
The read head includes a sensor that is located between nonmagnetic electrically insulative first and second read gap layers and the first and second read gap layers are located between ferromagnetic first and second shield layers. In recent read heads a spin valve sensor is employed for sensing magnetic fields from the rotating magnetic disk. The sensor includes a nonmagnetic conductive layer, hereinafter referred to as a spacer layer, sandwiched between first and second ferromagnetic layers, hereinafter referred to as a pinned layer, and a free layer. First and second leads are connected to the spin valve sensor for conducting a sense current therethrough. The magnetization of the pinned layer is pinned perpendicular to an air bearing surface (ABS) of the head and the magnetic moment of the free layer is located parallel to the ABS but free to rotate in response to external magnetic fields. The magnetization of the pinned layer is typically pinned by exchange coupling with an antiferromagnetic layer.
The spin valve sensor is characterized by a magnetoresistive (MR) coefficient, also known as giant magnetoresistance (GMR), that is substantially higher than the MR coefficient of an anisotropic magnetoresistive (AMR) sensor. MR coefficient is dr/R were dr is the change in resistance of the spin valve sensor and R is the resistance of the spin valve sensor before the change.
Because of high conductance (low resistance) and resistance to corrosion, gold (Au) is a desirable material for the first and second leads that are connected to the read sensor. Pure gold (Au), when used as conductor leads, however, presents a problem due to nodule formation of the gold at the ABS. This is due to pressure and high temperatures within the head during operating conditions of the read head within a magnetic disk drive. The operating temperatures can vary between 80.degree. C.-120.degree. C. Pressure on the leads increases with an increase in temperature due to expansion of layers adjacent the leads such as the first and second read gap layers and the first and second shield layers which are adjacent the read gap layers. With pressure due to the aforementioned temperatures the gold (Au), which is soft, is squeezed out of the leads at the ABS of the read head causing the aforementioned nodules. The nodules can short the leads to the first and second shield layers or short across edge portions of sensitive elements of the read sensor causing a failure of the read head. Because of the problems with gold (Au) leads have been made from tantalum (Ta) which does not have the nodule problem. Unfortunately, tantalum (Ta) has a significantly higher resistance than gold (Au) which results in increased heating of the read head unless the thickness of the tantalum (Ta) lead layers is increased. Unfortunately, an increase in thickness of the lead layers causes steps adjacent the read sensor which are replicated by subsequent layers all the way to the write gap which can cause the write gap of the write head to be curved. This is known in the art as write gap curvature and causes the write head to write curved magnetic impressions into tracks of a rotating magnetic disk which are then read by sensors that read straight across. This causes a reduction in the read signal which equates to less storage capacity of the magnetic disk drive.